Portion of an umbrella base



FIG. 1 is a top perspective view of a portion of an umbrella base showing our new design;

FIG. 2 is a left side elevational view thereof, the right side and front and rear being a mirror image;

FIG. 3 is a top plan view thereof;

FIG. 4 is an enlarged side elevational view thereof; and,

FIG. 5 is an enlarged top plan view thereof.

The circles shown in broken lines in FIGS. 3 and 5 represent the bounds of the claimed design while all other broken lines are directed to environment and are for illustrative purpose only. None of the broken lines form a part of the claimed design. 

CLAIM The ornamental design for a portion of an umbrella base, as shown and described. 